Despite frigid conditions in the East, U.S. seeing more record warmth this winter

The U.S. is experiencing one of the most unusual winters in years, with a pronounced and enduring bubble of warm, high pressure over the West, and blast after blast of frigid Arctic air and heavy snow in the eastern two-thirds of the country. The warmth is breaking all-time records, while the cold is rivaling some of the coldest weather in more than two decades.

Ski areas are struggling to stay open in California’s Sierra Nevada mountains in the face of a snowpack that has just 22% of its typical snow water equivalent for this time of year. Snow water equivalent measures the amount of water that would result from melting the snowpack, and is a crucial calculation for California’s water supply, which is highly dependent on winter snowfall in the mountains.

Meanwhile, organizers of Alaska’s legendary Iditarod sled-dog race were forced to change the start of its route from Anchorage to Fairbanks due to the lack of snow cover; this is only the second time in its 43-year history that such a route change has taken place.

In states east of the Rocky Mountains, though, the winter has been unrelentingly frigid and snowy, especially since January.

The Great Lakes, which set records for their ice cover last winter, are outpacing the freeze-up from a year ago. For example, nearly all of Lake Erie has frozen over, with parts of Niagara Falls becoming entombed in ice, though water is still flowing underneath.

Boston has received a whopping 8 feet of snow since mid-January alone, and is on pace to meet or beat its all-time record season of 1995 to 96. Boston’s blizzard blitz is unprecedented in its history of record-keeping, which dates back to the late 19th century.

This chart shows the pace of snowfall accumulation in Boston for this winter, to date, compared to the record-setting winter of 1995 to 96.

Image: Bob Al-Greene/Mashable

In parts of Maine, the snow depth is nearing 100 inches — and may even surpass that, by the time the next snowstorm is finished with the state on Friday.

Another Siberian invasion

The next wave of brutally cold air, with temperatures between 20 and 45 degrees below average for this time of year, has already crossed into the U.S. from Canada, and is destined to lead to record lows, from Illinois to Boston and possibly all the way into Georgia and Florida. Computer models are also showing a likelihood of yet another cold wave next week, as filaments of the tropospheric polar vortex — which is related to the polar vortex higher in the atmosphere — rotate south from near Greenland into the lower 48 states.

Based on an analysis of National Weather Service forecasts, nearly 75% of the lower 48 states are expected to see temperatures at or below 32 degrees Fahrenheit during the next seven days. This means that 221 million people will experience such cold temperatures, including residents of typically mild states, including Florida, Alabama and Louisiana.

A majority of the continental U.S. is expected to see temperatures reach at or below 10 degrees Fahrenheit during the same seven-day period, according to WeatherBell Analytics, a provider of weather data to the private sector.

What's more, 114 million people could see temperatures plunge to at or below 0 degrees Fahrenheit by early next week, including major metropolitan areas such as New York, Philadelphia, Chicago, Boston and St. Louis.

The Weather Channel reported that if the temperature in Nashville dips below 0 degrees on Thursday morning, it would be the latest this has occurred in the winter season since records began there in 1871.

Through the weekend, some locations from the Mid-Atlantic to the Carolinas may record their coldest temperatures since the mid-1990s, according to the NWS. The deep snowpack in some areas, including freshly fallen snow across the Mid-Mississippi Valley and Mid-Atlantic, will help lower temperatures further by radiating heat back into space more efficiently.

However, even with an unusually cold air mass and widespread snow cover, not many all-time cold temperature records are expected to be set. Instead, mostly daily and possibly monthly records are expected to be eclipsed.

It’s getting more difficult to break all-time cold-temperature records, in addition to monthly records, as the overall climate of the U.S. — along with the globe — warms in response to natural climate variability and increasing concentrations of greenhouse gases in the air. In fact, the frequency of extremely cold overnight low temperatures is expected to substantially decline in the coming decades.

Cold comfort: The Western warmth is winning

Although residents of the Midwest, South, and East Coast are justified in complaining about the seemingly never-ending cold and snow, so far this winter, the warmth in the West is outpacing the cold when it comes to record temperatures and overall endurance of the unusual temperatures.

According to data from the National Climatic Data Center (NCDC) in Asheville, North Carolina, there were 3,829 daily high temperature records set or tied in the U.S. during the past 30 days, as well as 3,368 record warm overnight low temperature records set or tied. This compares to just 498 records set or tied for the coldest high temperature, along with 386 daily records set or tied for the coldest low temperature.

Record high temperatures versus record lows for the Jan. 1-Feb. 17, 2015 period.

Image: Climate Central

A similar disparity is also visible in the monthly temperature records categories, with 278 monthly record highs set or tied, and no monthly records for the coldest high temperature.

Part of the reason why the West has been so warm can be found in the Northeast Pacific Ocean, where a large area of above-average water temperatures has helped spawn a resilient area of high pressure aloft that is acting as a block to advancing weather systems and cold air. This is leading to above-average temperatures across Alaska, where Sitka in the southeastern part of the state set a record high of 56 degrees Fahrenheit on Tuesday; this was warmer than most areas in the lower 48 states.

Seven Western states — California, Idaho, Nevada, Oregon, Utah, Washington and Wyoming — had a top-10 warmest month of January this year. What's more, the warmth has been accompanied by dry conditions, as well as relatively warm storm systems that have dumped snow only on the highest mountain peaks.

In San Francisco, no rain fell at the downtown observation station or the airport in January, the first time this happened since records began there in 1850. January is typically that city’s wettest month of the year, and the lack of rainfall has only heightened drought concerns.

The high pressure ridge — which has been present for all of 2015 and for much of last year — is causing the jet stream, which steers weather systems and separates air masses, to detour around the West, and turn sharply to the south across the Midwest and eastern U.S. This is allowing frigid temperatures from the North Pole and Siberia to turn Boston into a scene from The Day After Tomorrow, and shut down cities in the Southeast due to snow and ice this week.

“We’ve had, for months now — double-digit months — this persistent ridge in the west and troughiness in the east pattern,” Deke Arndt, chief of NCDC’s climate monitoring branch, said in an interview.

Projected winds at jet stream level on Feb. 22, 2015, showing a bulge in the jet, or ridge, over the Northwest, and a trough in the Central U.S. associated with another Arctic outbreak.

Arndt added that the nonstop warmth in the West has steadily built up more records, while the East has seen more transient cold-weather outbreaks in the wake of each storm system.

“It’s kind of a tortoise and the hare situation,” he said, with the West cast as the tortoise. “When you tally the statistics, the tortoise kind of wins in terms of the numbers.”

Arndt noted that neither the polar vortex cold waves of 2014, nor the Arctic outbreaks this year so far, have been breaking temperature records set in the extremely cold winters that occurred in the 1970s and 1980s. Instead, they’ve been eclipsing records from the past 10 to 20 years.

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